Methyl Complexes Research Articles

Polycomb Group Protein Yin Yang 1 Controls DNA Methylation in Murine T Lymphocyte Development

Transcription factors and epigenetic regulators play key functions in T lymphocyte lineage commitment and development. Mammalian PcG proteins are major negative regulators of gene expression that typically bind as large complexes (such as Polycomb Repressive Complex 1 (PRC1) and PRC2) to gene regulatory regions selectively targeted by an as yet unknown mechanism. While nearly all mammalian PcG proteins are lack of specific DNA binding capacities, transcription factor Yin Yang 1 (YY1) can bind at the DNA sites specifically and recruit other PcG proteins to specific DNA sequences. A small 25 amino acid YY1 domain (the REPO domain) is necessary and sufficient for the recruitment of PcG proteins, PcG-mediated stable transcriptional repression and histone modification. While YY1ΔREPO is competent for DNA binding, transcriptional activation, transient transcriptional repression and interaction with transcriptional coregulators such as HDACs, YY1ΔREPO is defective in all YY1 PcG functions. Our prior study demonstrated that deletion of YY1 in the hematopoietic system leads to T cell development blockage at the double-negative 3 (DN3) stage. Interestingly, ectopic expression of YY1∆REPO in YY1 null background by retroviral bone marrow transplantation could not rescue YY1 deficiency mediated T cell survival defect. This suggests that the YY1 REPO domain/PcG function plays a vital role in T cell development. Herein, we generated the YY1 REPO domain conditional knockout mouse model ( Yy1 f/∆REPO Vav-Cre) by CRISPR/Cas9 to further dissect the YY1 REPO domain/PcG function in T cell development. Yy1 f/∆REPO Vav-Cre ( Yy1 -/∆REPO) mice have reduced thymus weight and cellularity with medulla aplasia. Compared with wild-type (WT) and YY1 heterozygous ( Yy1 +/-) mice, Yy1 -/∆REPO mice have an increased percentage of DN3 cells with decreased DN4 percentage supporting a developmental blockage at the DN3 stage. Yy1 -/∆REPO DN T cells fail to go through TCRβ rearrangement with increased apoptosis and reduction of TCRβ + cells in the thymus compared with WT and Yy1 +/-cells. Interestingly, RNA-seq analysis in sorted primary DN3 cells revealed the genetic network governing DNA methylation, histone methylation, chromosome maintenance, and translation initiation complex formation are deregulated in Yy1 -/∆REPO mice compared to WT and Yy1 +/-mice. DN T cell development requires precise and dynamic regulation of histone and DNA methylation and demethylation. Interestingly, the DNA demethylase enzymes ten-eleven translocation (TET) family proteins Tet1 and Tet2 are downregulated in Yy1 -/∆REPO DN3 thymocytes compared with WT and Yy1 +/- DN3 cells. Our data show that the YY1 REPO domain/PcG function is required for DN3-DN4 transition via regulating TCRβ rearrangement and the YY1 REPO domain/PcG function plays a critical role in proper DNA methylation status in early T cell development. As PcG proteins modify histone via trimethylation of histone H3 on lysine 27, we will further assess the impact of YY1 REPO domain/PcG function on histone methylation in T cell development. By utilizing a powerful mouse model for identifying YY1 functions as PcG domain-dependent or PcG domain-independent, our study has generated fundamental new insights into the epigenetic landscape in T cell development.

Impact of Truncation on Optoelectronic Properties of Azaborole Helicenes.

Herein, we report configurationally stable singly-truncated (ST) and structurally flexible doubly-truncated (DT) helically chiral compounds derived from azabora[7]helicenes by a hypothetical removal of a single or two C=C double bonds. The singly-truncated constitutional isomers were synthesized from either benzoisoquinoline (BIQ) or phenantherene building blocks and the corresponding biaryls in excellent yields to give azabora[5]helicenes with a pendant phenyl ring at a sterically hindered position. These systems highlight the electronic impact of the nitrogen donor substitution position. The compounds with a disrupted BIQ moiety (STN) possess remarkable photoluminescence quantum yields of up to 0.53 in the solid state and a blue emission in solution with dissymmetry factors of up to ca. 3 × 10-3. Upon cooling to 79 K all compounds exhibit phosphorescence with lifetimes of up to ca. 0.5 s. A methyl complex of azabora[7]helicene showing excellent configurational stability was used as a chiral inducer embedded in an emissive polymer (F8BT) to produce circularly polarized organic light emitting diodes with an electroluminescence dissymmetry factor gEL of up to 0.54.

Synthesis of asymmetrical β-diketiminate magnesium methyl complexes and their catalytic application in cyanosilylation of ketones

Two asymmetrical β-diketiminate magnesium methyl complexes [(DippArNacnac)MgMe(THF)] have been synthesized in high yields and structurally characterized via single crystal X-ray diffraction etc. Subsequently, they have been successfully employed as highly efficient catalysts in the cyanosilylation of ketones including natural products with low catalyst loading (0.2 mol %) under the solvent-free condition at room temperature. A plausible mechanism was proposed base on the corresponding stoichiometric experiments and density functional theory (DFT) calculations.

Three-Coordinate Halide and Methyl Complexes of Chromium, Manganese, Iron, Cobalt, and Nickel Enabled by an Imidazolin-2-iminato Ligand

Three-Coordinate Halide and Methyl Complexes of Chromium, Manganese, Iron, Cobalt, and Nickel Enabled by an Imidazolin-2-iminato Ligand

Selective Zinc‐Catalyzed 1,2‐hydroboration of N‐heteroaromatics via a Non‐Hydride Mechanism

AbstractA novel bidentate amine‐imine ligand precursor LH has been synthesized. This compound was reacted with ZnMe2 to generate the zinc methyl complex, LZnMe (4). The latter compound was fully characterized by NMR spectroscopy and single crystal X‐ray diffraction. Compound 4 is a catalyst for the hydroboration and hydrosilylation of N‐heterocycles, but with moderate catalytic activity. A more active catalyst, the zinc hydride complex LZnH (5) was synthesized by reacting the lithium salt LLi with ZnCl2 followed by sequential reaction with tBuOK and PhMeSiH2. Compound 5 catalyzes the selective 1,2‐hydroboration of nitrogen heteroaromatics with decreased catalyst load and under mild conditions. Deuterium‐labeling experiments and kinetic studies provided insight into the possible reaction mechanism. It is proposed that hydride transfer to the substrate proceeds directly from the reductant (borane) via a six‐membered transition state facilitated by the catalyst, in which it plays an ambiphilic role, activating the substrate via coordination to the Lewis acidic zinc and enhancing the hydricity of the borane through coordination to the zinc hydride.

Arginine methylation of RNA-binding proteins is impaired in Huntington's disease.

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the HD gene, coding for huntingtin protein (HTT). Mechanisms of HD cellular pathogenesis remain undefined and likely involve disruptions in many cellular processes and functions presumably mediated by abnormal protein interactions of mutant HTT. We previously found HTT interaction with several protein arginine methyl-transferases (PRMT) enzymes. Protein arginine methylation mediated by PRMT enzymes is an important post-translational modification with an emerging role in neurodegeneration. We found that normal (but not mutant) HTT can facilitate the activity of PRMTs in vitro and the formation of arginine methylation complexes. These interactions appear to be disrupted in HD neurons. This suggests an additional functional role for HTT/PRMT interactions, not limited to substrate/enzyme relationship, which may result in global changes in arginine protein methylation in HD. Our quantitative analysis of striatal precursor neuron proteome indicated that arginine protein methylation is significantly altered in HD. We identified a cluster highly enriched in RNA-binding proteins with reduced arginine methylation, which is essential to their function in RNA processing and splicing. We found that several of these proteins interact with HTT, and their RNA-binding and localization is affected in HD cells likely due to a compromised arginine methylation and/or abnormal interactions with mutant HTT. These studies reveal a potential new mechanism for disruption of RNA processing in HD, involving a direct interaction of HTT with methyl-transferase enzymes and modulation of their activity, and highlighting methylation of arginine as potential new therapeutic target for HD.

The yeast RNA methylation complex consists of conserved yet reconfigured components with m6A-dependent and independent roles.

N6-methyladenosine (m6A), the most abundant mRNA modification, is deposited in mammals/insects/plants by m6A methyltransferase complexes (MTC) comprising a catalytic subunit and at least five additional proteins. The yeast MTC is critical for meiosis and was known to comprise three proteins, of which two were conserved. We uncover three novel MTC components (Kar4/Ygl036w-Vir1/Dyn2). All MTC subunits, except for Dyn2, are essential for m6A deposition and have corresponding mammalian MTC orthologues. Unlike the mammalian bipartite MTC, the yeast MTC is unipartite, yet multifunctional. The mRNA interacting module, comprising Ime4, Mum2, Vir1, and Kar4, exerts the MTC's m6A-independent function, while Slz1 enables the MTC catalytic function in m6A deposition. Both functions are critical for meiotic progression. Kar4 also has a mechanistically separate role from the MTC during mating. The yeast MTC constituents play distinguishable m6A-dependent, MTC-dependent, and MTC-independent functions, highlighting their complexity and paving the path towards dissecting multi-layered MTC functions in mammals.

The yeast RNA methylation complex consists of conserved yet reconfigured components with m6A-dependent and independent roles

N6-methyladenosine (m6A), the most abundant mRNA modification, is deposited in mammals/insects/plants by m6A methyltransferase complexes (MTC) comprising a catalytic subunit and at least five additional proteins. The yeast MTC is critical for meiosis and was known to comprise three proteins, of which two were conserved. We uncover three novel MTC components (Kar4/Ygl036w-Vir1/Dyn2). All MTC subunits, except for Dyn2, are essential for m6A deposition and have corresponding mammalian MTC orthologues. Unlike the mammalian bipartite MTC, the yeast MTC is unipartite, yet multifunctional. The mRNA interacting module, comprising Ime4, Mum2, Vir1, and Kar4, exerts the MTC’s m6A-independent function, while Slz1 enables the MTC catalytic function in m6A deposition. Both functions are critical for meiotic progression. Kar4 also has a mechanistically separate role from the MTC during mating. The yeast MTC constituents play distinguishable m6A-dependent, MTC-dependent, and MTC-independent functions, highlighting their complexity and paving the path towards dissecting multi-layered MTC functions in mammals.

Tuning the photoluminescence properties of SLE- and MRL-active tricarbonylrhenium(I) complexes through minor structural changes of the organic ligand

Solid-state luminescence properties depend on numerous parameters, including the molecular geometry and the intermolecular interactions that take place in the solid. To clarify the role played by these parameters on the photoluminescence (PL) properties of tricarbonylrhenium(I) complexes, four molecules incorporating a 3-(2-pyridyl)-1,2,4-triazole (pyta) ligand with appended phenylbenzoxazole (PBO) unit were compared. One or two methyl groups were inserted at different places of the organic ligand of the parent compound RePBO, resulting in three new complexes RePBO-Me1, RePBO-Me2 and RePBO-Me3. As shown by NMR, the presence of the methyl group(s) induced some changes in molecular flexibility, but the electronic effects were relatively weak. As a result, the electrochemical and optical properties were little impacted, and the four complexes behaved almost similarly in organic solution, in agreement with theoretical calculations. In contrast, marked differences appeared between the complexes when considering the aggregation-induced emission (AIE) effect, mainly due to the formation of tiny microcrystals in aqueous medium. In the same way, the three methylated complexes in the form of microcrystalline powders showed clear crystallization-induced emission enhancement (CIEE) with respect to solutions, but with distinct characteristics. They emitted less intensely and at longer wavelengths than the unsubstituted complex. Most likely, the methyl groups strongly affect the geometry and the packing mode of the molecules in the crystals, which influence the PL properties in the solid state. After grinding the powders, the emission spectra of the three methylated complexes were shifted to the red, although this shift was weaker than that previously observed for RePBO. This effect was almost reversible after THF fuming. It was attributed to transitions between the crystalline and amorphous phases. Remarkably, in the amorphous phase where molecules regain their mobility, the emission differences between the four complexes almost disappeared. It was then concluded that the amplitude of the mechanoresponsive luminescence (MRL) effect strongly depends on the geometry of the molecules in the pristine powder. This study is one more step toward the rational design of photoluminescent tricarbonylrhenium(I) complexes. More generally, it is also a good example of how very small structural modifications can drastically govern the PL and MRL properties.

Hypoxia-Responsive lncRNA AC115619 Encodes a Micropeptide That Suppresses m6A Modifications and Hepatocellular Carcinoma Progression.

A micropeptide encoded by lncRNA AC115619 impedes formation of the m6A methylation complex to lower m6A levels and reduce the growth of hepatocellular carcinoma.

In Vitro, In Silico, ADME and Theoretical Analysis of Mn(II) and Co(II) Complexes Derived from Methyl‐(Z)‐N′‐Carbamothioylcarbamohydrazonate Schiff Base Ligand

AbstractMn(II) and Co(II) complexes of methyl‐(Z)−N′‐carbamothioylcarbamohydrazonate Schiff base ligand were synthesized. The ligand and metal salts were taken in 2 : 1 stoichiometric ratio. All the synthesized complexes were characterized using elemental analysis, molar conductance, magnetic moment and various spectroscopic techniques (FT‐IR, UV/VIS, EPR) techniques. Elemental and spectroscopic results verified bidentate donor nature of the ligand and octahedral geometry of all the complexes. The non‐electrolytic nature of Mn(II) and Co(II) complexes were suggested by conductivity data analysis. In vitro antibacterial (E. coli and S. aureus) and antifungal (C. albicans and C. tropicalis) screening were achieved by employing agar well diffusion method which revealed better antimicrobial activity of Co(II) complexes than Mn(II) complexes. In silico SwissADME study predicted the drug‐likeness probability of ligand and complexes. The interaction of two bacterial proteins (E. coli and S. aureus) with compounds was also analyzed using molecular docking study, which corroborate the in vitro analysis.

Isolation and characterization of bis(silylene)-stabilized antimony(I) and bismuth(I) cations

Monovalent group 15 cations L2Pn + (L = σ-donor ligands, Pn = N, P, As, Sb, Bi) have attracted significant experimental and theoretical interest because of their unusual electronic structures and growing synthetic potential. Herein, we describe the synthesis of a family of antimony(I) and bismuth(I) cations supported by a bis(silylene) ligand [(TBDSi2)Pn][BArF4] (TBD = 1, 8, 10, 9-triazaboradecalin; ArF = 3,5-CF3-C6H3; Pn = Sb, (2); Bi, (3)). The structures of 2 and 3 have been unambiguously characterized spectroscopically and by X-ray diffraction analysis and DFT calculations. They feature bis-coordinated Sb and Bi atoms which exhibit two lone pairs of electrons. The reactions of 2 and 3 with methyl trifluoromethane sulfonate provide a approach for the preparation of dicationic antimony(III) and bismuth(III) methyl complexes. Compounds 2 and 3 serve as 2e donors to group 6 metals (Cr, Mo), giving rise to ionic antimony and bismuth metal carbonyl complexes 6–9.

Structure of Uranium(V) Methyl and Uranium(IV) Ylide Complexes

Syntheses of rare examples of U(V) methyl and U(IV) ylide complexes are reported. Reaction of the previously reported U(IV) imido complex [(C5Me5)2U(py)(═NMes)] (py = pyridine, and Mes = 2,4,6-Me3C6H2) with CuI forms the U(V) complex [(C5Me5)2U(I)(═NMes)]. Reaction of the iodo complex with MgMe2 produces the methyl complex [(C5Me5)2U(CH3)(═NMes)]. The methyl complex was reacted with CH2PPh3, surprisingly forming [(C5Me5)2U(CH2PPh3)(═NMes)], a U(IV) ylide. This is formed from a disproportionation of a transient U(V) carbene, leading to the U(IV) ylide and a U(VI) bis(imido) complex, [(C5Me5)2U(═NMes)2]. These complexes were characterized using spectroscopic methods (nuclear magnetic resonance, infrared, and ultraviolet–visible–nean infrared), SQUID magnetometry, and X-ray crystallography, and density functional theory calculations are used to compare the U(V) methyl with the targeted U(V) carbene ligands.

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis.

The application of bimolecular reductive elimination to the activation of iron catalysts for alkene-diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (MePDI)FeCH3 and (EtPDI)FeCH3 (RPDI = 2,6-(2,6-R2-C6H3N═CMe)2C5H3N), and the alkyl-substituted examples, (CyAPDI)FeCH3 (CyAPDI = 2,6-(C6H11N═CMe)2C5H3N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, (iPrPDI)FeCH3, has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N2 atmosphere, both (MePDI)FeCH3 and (EtPDI)FeCH3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [(MePDI)Fe(N2)]2(μ-N2) and [(EtPDI)Fe(N2)]2(μ-N2), respectively, while (iPrPDI)FeCH3 proved inert to C-C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, (RPDI)Fe(η4-C4H6) (R = Me, Et, iPr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N2 or butadiene to access a catalytically active iron compound.

Reductive Elimination Reactions in Gold(III) Complexes Leading to C(sp3)-X (X = C, N, P, O, Halogen) Bond Formation: Inner-Sphere vs SN2 Pathways.

The reactions leading to the formation of C-heteroatom bonds in the coordination sphere of Au(III) complexes are uncommon, and their mechanisms are not well known. This work reports on the synthesis and reductive elimination reactions of a series of Au(III) methyl complexes containing different Au-heteroatom bonds. Complexes [Au(CF3)(Me)(X)(PR3)] (R = Ph, X = OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br; R = Cy, X = Me, OTf, Br) were obtained by the reaction of trans-[Au(CF3)(Me)2(PR3)] (R = Ph, Cy) with HX. The cationic complex cis-[Au(CF3)(Me)(PPh3)2]OTf was obtained by the reaction of [Au(CF3)(Me)(OTf)(PPh3)] with PPh3. Heating these complexes led to the reductive elimination of MeX (X = Me, Ph3P+, OTf, OClO3, ONO2, OC(O)CF3, F, Cl, Br). Mechanistic studies indicate that these reductive elimination reactions occur either through (a) the formation of tricoordinate intermediates by phosphine dissociation, followed by reductive elimination of MeX, or (b) the attack of weakly coordinating anionic (TfO- or ClO4-) or neutral nucleophiles (PPh3 or NEt3) to the Au-bound methyl carbon. The obtained results show for the first time that the nucleophilic substitution should be considered as a likely reductive elimination pathway in Au(III) alkyl complexes.

Comparative study of CO2 insertion into pincer supported palladium alkyl and aryl complexes.

The insertion of CO2 into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO2 utilization. Here, we synthesize pincer-supported palladium complexes of the type (tBuPBP)Pd(alkyl) (tBuPBP = B(NCH2PtBu2)2C6H4-; alkyl = CH2CH3, CH2CH2CH3, CH2C6H5, and CH2-4-OMe-C6H4) and (tBuPBP)Pd(C6H5) and compare the rates of CO2 insertion into the palladium alkyl bonds to form metal carboxylate complexes. Although, the rate constant for CO2 insertion into (tBuPBP)Pd(CH2CH3) is more than double the rate constant we previously measured for insertion into the palladium methyl complex (tBuPBP)Pd(CH3), insertion into (tBuPBP)Pd(CH2CH2CH3) occurs approximately one order of magnitude slower than (tBuPBP)Pd(CH3). CO2 insertion into the benzyl complexes (tBuPBP)Pd(CH2C6H5) and (tBuPBP)Pd(CH2-4-OMe-C6H4) is significantly slower than any of the n-alkyl complexes, and CO2 does not insert into the palladium phenyl bond of (tBuPBP)Pd(C6H5). While (tBuPBP)Pd(CH2CH3) and (tBuPBP)Pd(CH2CH2CH3) are resistant to β-hydride elimination, we were unable to synthesize complexes with n-butyl, iso-propyl, and tert-butyl ligands due to β-hydride elimination and an unusual reductive coupling, which involves the formation of new C-B bonds. This reductive process also occurred for (tBuPBP)Pd(CH2C6H5) at elevated temperature and a related process involving the formation of a new H-B bond prevented the isolation of (tBuPBP)PdH. DFT calculations provide insight into the relative rates of CO2 insertion and indicate that steric factors are critical. Overall, this work is one of the first comparative studies of the rates of CO2 insertion into different metal alkyl bonds and provides fundamental information that may be important for the development of new catalysts for CO2 utilization.

Controlled reduction of isocyanates to formamides using monomeric magnesium.

This work describes a transition metal-free methodology involving an efficient and controlled reduction of isocyanates to only formamide derivatives using pinacolborane (HBpin) as the hydrogenating agent and a bis(phosphino)carbazole ligand stabilized magnesium methyl complex (1) as the catalyst. A large number of substrates undergo selective hydroboration and give exclusively N-boryl formamides.

The regulation of m6A-related proteins during whole-body freezing of the freeze-tolerant wood frog.

Rana sylvatica (also known as Boreorana sylvatica) is one of the few vertebrates that spend extreme winters showing no physiological signs of life. Up to 70% of the total body water of the wood frog freezes as extracellular ice. Survival in extreme conditions requires regulation at transcriptional and translational levels to activate prosurvival pathways. N6-methyladenosine (m6A) methylation is one of the most common RNA modifications, regulating transcript processing and translation by executing important functions that affect regulatory pathways in stress conditions. In the study, regulation of m6A-related proteins in the liver of R. sylvatica was analyzed during 24h frozen and 8h thaw conditions. Decreases in the activity of demethylases of 28.44±0.4% and 24.1±0.9% of control values in frozen and thaw tissues, respectively, were observed. Total protein levels of m6A methyltransferase complex components methyltransferase-like 14 and Wilm's tumor associated protein were increased by 1.28-fold and 1.42-fold, respectively, during freezing. Demethylase fat mass and obesity, however, showed a decreasing trend, with a significant decrease in abundance during recovery from frozen conditions. Levels of mRNA degraders YTHDF2 and YTHDC2 also decreased under stress. Overall, increased levels of m6A methylation complex components, and suppressed levels of readers/erasers, provide evidence for the potential role of RNA methylation in freezing survival and its regulation in a hypometabolic state.

Ash2l, an obligatory component of H3K4 methylation complexes, regulates neural crest development

The vertebrate nervous system develops from embryonic neural plate and neural crest. Although genetic mechanisms governing vertebrate neural development have been investigated in depth, epigenetic regulation of this process remains less understood. Redundancy of epigenetic factors and early lethality of animals deficient in critical epigenetic components pose major challenges in characterization of epigenetic factors in vertebrate neural development. In this study, we use the amphibian model Xenopus laevis to investigate the roles of non-redundant, obligatory components of all histone H3K4 activating methylation complexes (COMPASS, also known as SET1/MLL complexes) in early neural development. The two genes that we focus on, Ash2l and Dpy30, regulate mesendodermal differentiation in mouse embryonic stem cells and cause early embryonic lethality when removed from mouse embryos. Using targeted knockdown of the genes in dorsal ectoderm of Xenopus that gives rise to future nervous system, we show here that ash2l and dpy30 are required for neural and neural crest marker expression in Xenopus late neurula embryos but are dispensable for early neural and neural plate border gene expression. Co-immunoprecipitation assays reveal that Dpy30 and Ash2L associate with the neural plate border transcription factors, such as Msx1 and Tfap2a. Chromatin immunoprecipitation (ChIP) assay further demonstrates that Ash2L and the H3K4me3 active histone mark accumulate at the promoter regions of the neural crest gene sox10 in a Tfap2a-dependent manner. Collectively, our data suggest that Ash2l and Dpy30 interact with specific transcription factors to recruit COMPASS complexes to the regulatory regions of neural crest specification genes to control their expression and influence development of the nervous system during vertebrate embryogenesis.

Iridium Complexes with a Naphthyridine-Based Si,N-Ligand: Synthesis and Catalytic Activity toward Olefin Hydrogenation

16-Electron iridium complexes bearing a silyl-1,8-naphthyridine-based bidentate ligand (napySi), Ir(κ2Si,N-napySi)(H)(coe)X [X = Cl (1) and Me (2)], were synthesized and characterized. Single-crystal X-ray diffraction studies revealed that both 1 and 2 have a square-pyramidal geometry with the silyl moiety occupying the apical position and the nitrogen lone pair of napySi adjacent to the vacant metal center. Methyl complex 2 catalyzed hydrogenation of alkenes with H2 (1 atm) at room temperature. This hydrogenation proceeded significantly faster than that catalyzed by a related complex with no nitrogen lone pair adjacent to the metal. Based on this result, we suggest a possible catalytic cycle including cooperative activation of H2 between the nitrogen lone pair and the metal center for this system.